1. Field of the Invention
The present invention relates to a compact impact drive actuator that stepwise drives a movable body.
2. Description of the Related Art
There is known an actuator that supplies a sawtooth wave drive pulse to an electromechanical conversion device coupled to a drive shaft to displace the drive shaft along its shaft to thereby move a movable member friction-coupled to the drive shaft along its shaft. Such an actuator is called an impact drive actuator.
The operation principle of the impact drive actuator will be described. The impact drive actuator has a vibrator whose one end is fixed to a fixing member and the other end thereof is attached to a vibrating member serving as a drive shaft. A movable body is friction-coupled to the vibrating member so as to be movable in the vibration direction of the vibrator. In such a configuration, a sawtooth wave drive pulse is applied to the vibrator.
More specifically, firstly, a gradually increased voltage is applied to the vibrator. The vibrator is then displaced and, at the same time, the vibrating member is displaced. The gradual displacement of the vibrator allows the movable body to be moved together with the vibrating member due to friction with the vibrating member. Secondly, a rapidly reduced voltage is applied to the vibrator. The position of the vibrator is then returned to the original position and, at the same time, the vibrating member rapidly returns to its own initial position. At this time, slippage is caused between the movable body and vibrating member, so that the movable body stays at the same position. By applying the sawtooth wave drive pulse including a gradually increased voltage and rapidly reduced voltage to the vibrator as described above, the movable body is moved from one point to another. When the above operation is repeated, the movable body can intermittently be moved relative to the fixing member. To move the movable body in the reverse direction, a sawtooth wave drive pulse including a rapidly increased voltage and gradually reduced voltage is applied to the vibrator.
An actuator that uses the above drive principle is disclosed in U.S. Pat. No. 5,225,941. In this patent, the impact drive actuator is applied to a camera lens drive mechanism. A movable body serving as a lens barrel is fitted to a vibrating member. Further, an elastic member having a bent portion is attached to the movable body at the fitting portion. In this case, the bent portion of the elastic member is brought into pressure contact with the vibrating member to generate an adequate frictional force.
Another example is disclosed in U.S. Pat. No. 5,589,723. In an actuator disclosed in this patent, a friction adjuster including a vibrator is used for a portion that generates friction. By synchronizing a voltage applied to the generator of the friction adjuster and a voltage applied to a vibrator for displacing a vibrating member with each other, an appropriate frictional force for a movable body to be moved is obtained.